With the development of researches on the high power, high repetitive frequency pulsed power technology in China and the rising capacity of pulsed power system, there are stronger demands for better working performances of pulsed power switches, such as its delay time, current capacity, high frequency interruption capacity, lifetime, and so on. The widely used pulsed power switches mainly include triggered gas switches and triggered vacuum switches these years, and the trigger methods of these switches can be divided as electrical impulse triggered and pulsed laser triggered. The electrical triggered switches adopt trigger electrode placed in main gap to generate initial plasma by impulsive discharge, and closing the switch. The preferable trigger performances of electrical triggered switches need relative higher under voltage ratio and larger trigger voltage, limiting its application fields and the miniaturization of its trigger system. And there are severe arc ablation effects on the trigger electrodes and the coating materials on trigger electrodes after the closing of electrical triggered switches, affecting its closing performances and lifetime. Laser triggered switches adopt pulsed laser as trigger source, electrically insulated the trigger system with the main gap. And the main gap can be closed with the initial plasma generated by the interactions of high energy laser beam with targets. Compared to electrical triggered method, laser triggered switches can avoid the arc ablations on trigger electrode, and show many advantages, such as shorter delay time, higher trigger accuracy, easily controlled, repetitive triggered, and so on. Thus the high power, high repetitive frequency pulsed power systems generally employ laser triggered method.
Most of laser triggered gas switches adopt the electronegative gases with better insulation capacity as its insulation and arc interruption dielectrics, for example SF6 gas, and delay time of the switches can be controlled within dozens of nanoseconds. To satisfy the requirements for switches with better working performances in high voltage, high power pulsed power system, the MV level laser triggered multi-stage multi-channel gas switches composed of series connected laser triggered gas gap and multi-stage self-breakdown gas gaps are proposed by researchers. And the switches normally adopt gas mixtures of SF6/N2 as its insulation and arc interruption dielectric. Instantaneous power of the switches can reach terawatt level, and the delay time can be controlled within 10 ns. But limited by the properties of SF6 gas, the repetitive frequency performances of switches are unsatisfied. And the working performances of switches are also affected by the decomposed SF6 gas during arcing process, thus the insulation gas needs to be replaced regularly, raising the cost of gas switches.
Laser triggered vacuum switches adopt vacuum as its insulation and interruption dielectric, and shows many advantages, such as with larger current capacity, higher reliability, proper repetitive frequency performances, maintenance-free, and so on, and the better trigger performances can be obtained compared to laser triggered gas switches under same working conditions. Researches on high power laser triggered switches these years mainly concentrate on laser triggered gas switches, few works pay attention to high voltage, high power laser triggered vacuum switches. Due to the nonlinear growth relationships between vacuum gap distance and withstand voltage, the developments of high voltage laser triggered vacuum switch are limited. Based on the researches on multi-break vacuum circuit breakers and laser triggered multi-stage gas switches, laser triggered multi-stage vacuum switch composed of laser triggered vacuum gap and multi-stage self-breakdown vacuum gaps are proposed. The distance of serial vacuum gaps, the structures of electrodes, and trigger system can be properly designed and configured to satisfy the requirements of pulsed power switches with higher operating voltage and better trigger performances. The switch utilizes the trigger advantages of laser triggered vacuum gap and the insulation and arc interruption capacity of short vacuum gaps, enhancing the working performances of pulsed power switches and decreasing the maintenance costs.